سیاست های مدیریت منابع در سیستم های GPRS

In this paper we consider the problem of resource management in GSM/GPRS cellular networks offering not only mobile telephony services, but also data services for the wireless access to the Internet. In particular, we investigate channel allocation policies that can provide a good tradeoff between the QoS guaranteed to voice and data services end users, considering three different alternatives, and developing analytical techniques for the assessment of their relative merits. The first channel allocation policy, voice priority, gives priority to voice in the access to radio channels; we show that this policy cannot provide acceptable performance to data services, since when all the channels are busy with voice connections, data services perceive long intervals of service interruption. The second channel allocation policy is called R-reservation; it statically reserves a fixed number of channels to data services, thus drastically improving their performance, but subtracting resources from voice users, even when these are not needed for data, thus inducing an unnecessary performance degradation for voice services. The third channel allocation policy is called dynamic reservation; as the name implies, it dynamically allocates channels to data when necessary, using the information about the queue length of GPRS data units within the base station. A threshold on the queue length is used in order to decide when channels must be allocated to data. Numerical results show that the dynamic reservation channel allocation policy can provide effective performance tradeoffs for data and voice services, with the additional advantage of being easily managed through the setting of the threshold value.

The successes of mobile telephony on one side, and Internet services on the other, are producing very high expectations for the commercial success of wireless Internet access services. Mobile telephony companies in Europe have made huge investments in this sector to acquire UMTS (Universal Mobile Telecommunications System) licenses, and are already offering data services over their existing GSM (Global System for Mobile Communications) networks, so as to start building the market, which will hopefully expand with the advent of UMTS and the proliferation of IEEE 802.11 Wireless LAN islands. The technology that is now becoming available to integrate packet data services into GSM networks is GPRS (Generalized Packet Radio Service). The fact that GPRS exploits the same resources used by mobile telephony raises a number of questions concerning the dimensioning and the management of the GSM/GPRS radio interface. In this paper we tackle this issue, and discuss three possible approaches to manage the radio interface in a GSM/GPRS cell, providing analytical models for their performance analysis, as well as numerical performance results that provide insight into the relative merits of the alternate approaches. The paper is organized as follows. In Section 2 we describe the characteristics of the GSM/GPRS cellular mobile communication network that we consider, together with the probabilistic assumptions that are needed to describe the system dynamics with Markovian models. In the same section we also describe the three channel allocation policies which will be analyzed and compared in the following sections. After a short discussion on related work in Section 3 we present the analytical models and their solutions in Section 4. Some numerical results are shown and discussed in Section 5. Section 6 concludes the paper.

In this paper we have investigated channel allocation policies for GSM/GPRS cellular networks offering not only mobile telephony services, but also data services for the wireless access to the Internet. Three different alternatives were described, developing simple Markovian models for the assessment of their relative merits. Numerical results showed that the voice priority policy, that gives priority to voice in the access to radio channels, cannot provide acceptable performance to data services. The R-reservation policy, that statically reserves a fixed number of channels to data services, was shown to drastically improve their performance, but to exact a rather high toll in terms of the voice services QoS. This is specially annoying because this policy subtracts resources from voice users even when these are not needed for data, thus inducing an unnecessary performance degradation for voice services. Instead, the dynamic reservation policy, that dynamically allocates channels to data only when necessary, using the information about the queue length of GPRS data units within the base station, was shown to provide very effective performance tradeoffs for data and voice services, with the additional advantage of being easily managed through the setting of the threshold value that triggers the dynamic allocation of channels to data. A further advantage of the dynamic reservation scheme is the fact that it tries to allow a full exploitation of the system resources by voice traffic when no data traffic is present, but it gradually allocates resources to data, so as to guarantee the data services QoS. This may be an extremely attractive feature of the scheme in a scenario where wireless network operators generate most of their revenues with voice services, but are eager to carry data traffic with acceptable QoS, so as to be able to open a new market of mobile data services for the wireless access to the Internet.